1. Technical Field
The present invention relates to techniques for preventing burn-in of electro-optical devices.
2. Related Art
Generally, in electro-optical devices, such as liquid crystal displays, in order to prevent application of a DC component to a liquid crystal capacitor (pixel) formed by holding liquid crystal between a pixel electrode and a counter electrode, basically, AC driving is employed, i.e., the voltage applied to the pixel electrode is alternated between a higher (positive-polarity) voltage and a lower (negative-polarity) voltage.
Furthermore, in the case of active-matrix driving, in which pixel electrodes are driven by thin-film transistors (hereinafter referred to as “TFTs”), pushdown (also referred to as field through) or the like occurs.
Thus, if the reference voltage for defining the voltage applied to the pixel electrode is chosen to be the same as the voltage applied to the counter electrode, the effective value of voltage stored in the liquid crystal capacitor differs between cases of positive-polarity and negative-polarity voltages even if the positive-polarity and negative-polarity voltages correspond to the same pixel level. This causes application of a DC component to the liquid crystal capacitor.
If a DC component is applied to the liquid crystal capacitor, the liquid crystal could be degraded so that a still picture displayed previously appears as an afterimage. Since this afterimage is similar to burn-in that occurs on the fluorescent surface of a cathode-ray-tube (CRT) display, the phenomenon caused by application of a DC component to the liquid crystal capacitor is sometimes called burn-in Furthermore, the difference in the effective value of voltage at the liquid crystal capacitor causes a difference in the pixel level brightness) of the pixel, and this might cause flicker in an image displayed.
In order to overcome this problem, techniques have been proposed in which the voltage of the counter electrode is adjusted so that flicker will be minimized when positive-polarity and negative-polarity voltages corresponding to the same pixel level are applied alternately (e.g., see JP-A-2005-225169).
However, in some cases, is not possible to prevent application of a DC component to the liquid crystal capacitor simply by adjusting the voltage of the counter electrode. Furthermore, it is not possible to prevent application of a DC component flexibly.